The present invention relates to a magnetic sensor, and particularly it relates to a magnetoresistive sensor such as a reproducing magnetic head which uses a magnetoresistive element suited for a magnetic recording system such as a magnetic disk system or a magnetic tape system.
In a conventional magnetoresistive sensor, as disclosed in the Specification of the U.S. Pat. No. 3,940,797, a magnetoresistive film is formed on high permeability magnetic ferrite (Ni-Zn or Mn-Zn ferrite) with an insulating film of SiO.sub.2, Al.sub.2 O.sub.3 or the like interposed between them. The magnetoresistive film generates a very large quantity of heat, since high current of 10.sup.5 to 10.sup.6 A/cm.sup.2 or above is applied thereon. The high permeability magnetic ferrite has a very low heat conductivity. Therefore the temperature of the element is increased by the heat and this causes the deterioration of characteristics. However, no consideration has been given heretofore to rapidly releasing a high heat caused thereby and keeping the element at low temperature.
Moreover, the aforesaid ferrite, which is used as a magnetic shield, is bulky ferrite which has a saturation flux density of 0.5 T at the highest and a permeability of about 200 to 300 at the most at 10 MHz, and thus flux from a magnetic recording medium scatters into the whole ferrite at low density. Therefore, the flux density in the vicinity of a magnetic gap is low. In this connection, no consideration has been given to making a reproduced waveform from the magnetoresistive film sharp, though the waveform therefrom is broad.